It was a make-or-break moment for Zuckerberg with the eyes of the tech and political worlds on the blockbuster hearing.

Here are some key moments:

Zuckerberg says he's sorry: "It's clear now that we didn't do enough to prevent these tools from being used for harm," Zuckerberg said.

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"That goes for fake news, foreign interference in elections, and hate speech, as well as developers and data privacy. We didn't take a broad enough view of our responsibility, and that was a big mistake," he continued.

"It was my mistake, and I'm sorry. I started Facebook, I run it, and I'm responsible for what happens here."

Zuckerberg says Mueller has interviewed Facebook employees: Zuckerberg told Sen. Patrick Leahy (D-Vt.) that special counsel Robert Mueller has interviewed Facebook employees as part of his investigation into Russian interference.

The Facebook CEO also said he "believes" the company may have been served with a subpoena from the special counsel's office.

"I want to be careful here because our work with the special counsel is confidential," Zuckerberg said Tuesday. "I know that we are working with them."

Facebook stock soared during testimony: Wall Street reacted favorably to Zuckerberg's performance on Tuesday. Facebook shares closed up 4.5 percent on Tuesday during Zuckerberg's testimony, rallying to their highest points on the day, during his hearing.

"We considered it a closed case," Zuckerberg said. "In retrospect, that was a mistake."

'Your user agreement sucks': Zuckerberg also received a scolding from Sen. John KennedyJohn Neely KennedyMORE (R-La.) who argued Facebook's user agreement was too complicated for the average American to know what they were signing up for.

"Here's what everybody's been trying to tell you today and I say this gently," Kennedy said. "Your user agreement sucks. The purpose of that user agreement is to cover Facebook's rear end, it's not to inform users of their rights."

CARDBOARD ZUCKS: The hearing dominated much of Washington's attention. Even before it began, an advocacy group called Avaaz placed dozens of cardboard cutouts of Zuckerberg on the Capitol lawn.

"The group is calling on the CEO to ban all bots, alert the public any and every time users see fake or disinformation, fund fact checkers around the world, and submit to an independent audit to review the scale and scope of fake news," Avaaz said in a press release.

"Facebook has made billions of dollars selling advertisements targeted to its customers, and in this instance made millions selling advertisements to political campaigns that developed those very ads on the back of their customers' own stolen personal information," Richard Fields, one of the attorneys for the defendants, said in a statement. "That's unacceptable, and they must be held accountable."

The seven plaintiffs were among the 87 million Facebook users whose data was handed over to Cambridge Analytica without their knowledge or consent.

Facebook's response: "We are committed to vigorously enforcing our policies to protect people's information," Paul Grewal, Facebook's deputy general counsel, said in a statement. "We will take whatever steps are required to see that this happens."

TWITTER ENDORSES HONEST ADS ACT: Twitter on Tuesday backed a bill that would require greater transparency around online political ads.

"@Twitter just joined @Facebook and announced support of my bill to require social media companies to post paid political ads and require disclaimers. We need to hold tech companies to same rules as everyone else. #HonestAdsAct #Progress Need to hear from @google," Klobuchar wrote on Twitter.

Facebook has also backed the legislation, and Democrats urged Zuckerberg on Tuesday to promote it.

UBER TO BUY BIKE-SHARING COMPANY: Uber announced Tuesday that it's acquiring JUMP, a bike-sharing company that operates in Washington, D.C. and San Francisco.

"We're committed to bringing together multiple modes of transportation within the Uber app--so that you can choose the fastest or most affordable way to get where you're going, whether that's in an Uber, on a bike, on the subway, or more," CEO Dara Khosrowshahi said in a blog post.

REDDIT FOUND NEARLY 1,000 RUSSIA-LINKED ACCOUNTS: Reddit CEO Steve Huffman said on Tuesday that the company had found 944 accounts linked to the Internet Research Agency, a Russian troll farm alleged to have waged a disinformation campaign ahead of the 2016 election.

In a post, Huffman said that few of the accounts "had a visible impact on the site."

LONGREAD OF THE DAY: All eyes are Facebook's woes with Cambridge Analytica with Zuckerberg testifying. But Facebook is also in hot water for some of its practices abroad. BuzzFeed details how Facebook is being used to incite violence against Muslims in Sri Lanka.

ON TAP:

Zuckerberg's none done yet. The House Energy and Commerce Committee will hold a hearing with the Facebook CEO testifying at 10:00 a.m.

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